Solar-thermal collector

ABSTRACT

A solar-thermal collector formed by an upper plastic layer facing solar rays and by a lower plastic layer not facing the solar rays, whereby between the two secured together plastic layers there is formed at least one hollow chamber for passage of a heat-transport medium. The upper plastic layer is transparent, and an inner surface of the upper plastic layer, which inner surface faces the hollow chamber, has an absorbing layer.

FIELD OF THE INVENTION

[0001] The invention relates to a solar-thermal collector having acollector housing which is formed by an upper plastic layer facing solarrays and a lower plastic layer not facing the solar rays, wherebybetween the two plastic layers there is formed at least one hollowchamber for passage of a heat-transport medium, in particular water.

BACKGROUND OF THE INVENTION

[0002] Such a solar-thermal collector is known from the DE 196 06 293A1. The solar-thermal collector has a collector housing which is formedof two molded plastic panels which are welded together. The two plasticpanels form a hollow chamber through which water flows during theoperation of the solar-thermal collector. An upper plastic panel facesthe solar rays during operation. The lower plastic panel does not facethe solar rays and is usually fastened to a suitable building wall. Thelower plastic panel is tinted, whereas the upper plastic panel istransparent. Thus, the heat conversion of the solar rays takes place inthe area of the lower, tinted plastic panel. A heat loss on the surfaceof the collector should in this manner be reduced.

[0003] A solar-hose collector is known from the DE 37 03 856 A1, whichcollector has a plastic hose. The plastic hose is transparent over aportion of its circumference by being manufactured by coextrusion out ofa transparent plastic on the one side and a dark, absorbing plastic onthe other side.

[0004] However, practice has shown in the case of this collector thatmicroorganisms form and settle inside of the hollow chamber on thelower, tinted plastic panel. This can lead to an undesired contaminationof the water and a formation of a putrefying substance.

[0005] The purpose of the invention is to produce a solar-thermalcollector of the above-identified type, where contaminations can beavoided and which nevertheless operates efficiently.

SUMMARY OF THE INVENTION

[0006] This purpose is attained by the upper plastic layer being of atransparent design, and by providing an inner surface of the upperplastic layer, which inner surface faces the hollow chamber, with asolar ray absorbing layer.

[0007] The absorbing layer absorbs the solar rays and converts them intoheat. The absorbing layer is relatively thin in design and haspreferably a thickness of between 0.1 mm and 0.5 mm. According to theinventive solution, the plastic material of the upper plastic layer isoriented relative to the solar rays above the absorbing layer and servesas an insulator so that the heat converted by means of the absorbinglayer can be taken along directly by the heat-transport medium. Theabsorbing layer is thin in comparison to the thickness of the plasticlayer in order to guarantee a low heat resistance. Contaminations ordeposits can also be reliably avoided. It is also possible to cover theabsorbing layer on the inner side facing the hollow chamber additionallywith a protective foil in order to also avoid in this manner damage toor contaminations of the absorbing layer over a long time period.

[0008] The absorbing layer is in a further development of the inventioncoextruded with the upper plastic layer. This is a particularlyeconomical manufacturing method.

[0009] The absorbing layer is in a further development of the inventionlaminated onto the inner surface of the upper plastic layer. This is analternative preferred solution for applying the absorbing layer onto theinner side of the upper plastic layer.

[0010] The lower plastic layer is in a further development of theinvention designed at least partially ray-absorbing. The lower plasticlayer is preferably tinted. Since the upper absorbing layer isrelatively thin, solar rays can still penetrate through said layer,which solar rays are then additionally converted into heat at the lowerplastic layer. This can further improve the efficiency of the collector.

[0011] The lower plastic layer is in a further development of theinvention designed transparent. This alternative solution also resultsin an excellent function of the collector and involves a slightly lowermanufacturing expense since the plastic does not need to be tinted. Inaddition, the collector housing is optically very becoming due to thetransparent design of the lower plastic layer.

[0012] The upper and the lower plastic layer are welded together in afurther development of the invention. The welding enables a completesealing off of the at least one hollow chamber of the collector andrepresents an extremely secure and uniformly sealed connection.

[0013] The upper plastic layer is in a further development of theinvention manufactured out of a different plastic material than thelower plastic layer. The upper plastic layer is preferably manufacturedout of polycarbonate. Also the absorbing layer consists of apolycarbonate. The upper plastic layer has advantageously a highertemperature stability than the lower plastic layer. Polycarbonate istemperature-stable up to approximately 150° C.

[0014] The lower plastic layer can preferably be manufactured out ofacrylonitrile-butadiene-styrene (ABS). ABS and polycarbonate (PC) can bewelded to one another. However, ABS is significantly less expensive.Since the thermal load for the lower plastic layer is not so high, samealso does not need to have as high a temperature stability as the upperplastic layer. However, ABS can be welded significantly better than PC.The lower plastic layer thus contributes significantly to the creationof a good and secure welding to the upper plastic layer. Due to thereduced temperature stability of the lower plastic layer same is lessexpensive, thus making it possible to keep the total manufacturingexpenses of the collector housing low.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Further advantages and characteristics of the invention resultfrom the claims. One preferred exemplary embodiment of the inventionwill be described hereinafter and is illustrated in the drawings, inwhich:

[0016]FIG. 1 is a top view of one embodiment of an inventivesolar-thermal collector,

[0017]FIG. 2 is a greatly enlarged, partially cross-sectionalillustration of a section II-II of the collector housing according toFIG. 1, and

[0018]FIG. 3 is a sectional view taken along the line III-III of FIG. 1.

DETAILED DESCRIPTION

[0019] A solar-thermal collector 1 according to FIGS. 1-3 correspondswith respect to its basic design to a conventional solar-thermalcollector, as it is known from the DE 196 06 293 A1. The solar-thermalcollector 1 has an undulating one piece upper plastic layer 1 a, asshown in FIG. 3, facing rays S (FIG. 2) and a flat lower plastic layer 1b facing away from the rays S which, corresponding to the disclosure inthe DE 196 06 293 A1, are molded plastic panels that are welded to oneanother as at 6 in an outer annular boundary area 4 as well as at eachof the plural locations 7 whereat each of the undulations of the upperlayer la touch the lower layer 1 b along a line as shown in FIG. 3. Thecollector 1 has an inlet nozzle 2 for a heat-transport medium in theform of water and an outlet nozzle 3, which nozzles are connected to asuitable, not illustrated water-circulation system. Regarding thegeneral characteristics of the solar-thermal collector, reference isadditionally made to the disclosure in the DE 196 06 293 A1.

[0020] The two plastic layers 1 a and 1 b form a hollow chamber H and aplurality of side-by-side passageways through which water flows when thecollector is in operation. The inner side of the upper plastic layer 1a, which inner side faces the hollow chamber H and the plurality ofpassageways, has an absorbing layer 5 which has preferably a thicknessof between 0.2 mm and 0.3 mm. The absorbing layer 5 extends continuouslyover the inwardly facing surface of the upper layer 1 a. The absorbinglayer 5 is also made of plastic, in the present case of PC. Theabsorbing layer 5 is in the illustrated exemplary embodiment during themanufacture of the plastic panel for the plastic layer 1 a coextrudedwith same, thus resulting already during the manufacture in a flat,integral and/or bonded connection of the absorbing layer 5 to the upperplastic layer 1 a. The absorbing layer 5 converts the solar rays Sentering through the transparent upper plastic layer 1 a into heat andconducts or heat exchanges such heat to the passing water.

[0021] The upper plastic layer 1 a acts as an insulating body for theabsorbing layer 5.

[0022] The lower plastic layer 1 b is manufactured in the illustratedexemplary embodiment out of a different plastic, namely out of ABS. Samecan be tinted, partially transparent or also nontransparent, light ordark. Since the solar rays S are at least to a large part alreadyconverted into heat through the upper absorbing layer 5, the lowerplastic layer 1 b is no longer subjected to a large thermal load.

[0023]FIG. 2 schematically illustrates a welding seam 6, by means ofwhich the upper and the lower plastic layers 1 a and 1 b with theabsorbing layer 5 sandwiched therebetween are welded throughout andsecurely to one another in the outer annular boundary area 4. It is tobe recognized that the absorbing layer 5 is also sandwiched between theupper layer 1 a and lower layer 1 b at each of the welding seams 7. Thesolar-thermal collector is utilized in particular on outside walls ofbuildings, namely in the roof area or in the facade region facing thesun, and is used in particular as a source for hot water.

What is claimed is:
 1. A solar-thermal collector with a collectorhousing formed by an upper plastic layer facing solar rays and by alower plastic layer not facing the solar rays, whereby between the twoplastic layers there is formed at least one hollow chamber for passageof a heat-transport medium, wherein the upper plastic layer has atransparent design, and wherein an inner surface of the upper plasticlayer, which inner surface faces the hollow chamber, has an absorbinglayer.
 2. The collector according to claim 1, wherein the absorbinglayer is integral and/or bonded with the upper plastic layer.
 3. Thecollector according to claim 1, wherein the absorbing layer is laminatedonto the inner surface of the upper plastic layer.
 4. The collectoraccording to claim 1, wherein the lower plastic layer is configured atleast partly ray-absorbing.
 5. The collector according to claim 1,wherein the lower plastic layer is transparent.
 6. The collectoraccording to claim 1, wherein the upper and the lower plastic layers arewelded to one another.
 7. The collector according to claim 6, whereinthe upper plastic layer is manufactured out of a different plasticmaterial than the lower plastic layer.
 8. The collector according toclaim 1, wherein the heat-transport medium is water.